Electric fluid heater



JAan. 13, 1959 E. c. KOCH ETAL 2,868,944

` ELECTRIC FLUID HEATER Film1 June 12; 1957 7 sheets-sheet 1 V nl m2 wwww Nv ENE EN www@ ATTORNEY Jan. 13, 1959 E. c. KOCH ET AL ELECTRIC FLUIDHEATER 7 Sheets-Sheet 2 Filed June 12, 1957 INVENTORS fl/GE/VE C`` KOCHKfz. w/v Z RA Y ATTORNEY N ////w j Jan. 13, 1959 E. c. KOCH ETALVELECTRIC FLUID HEATER Filed .mmev 12, 1957 7 Sheets-Sheet 3 Jari. 13,1959 E. c. KOCH ET AL `2,868,944 ELECTRIC FLUID HEATER 7 Sheets-Sheet 4Filed June 12K, 1957 lNvr-:N ORS EUGENE KOC/l KELw/v J.' PAY ATTORNEYJan. 13, 1 959 E. c. KocH ETA; 2,868,944

v ELECTRIC FLUID HEATER Filed June 12, 1957" E 7 sheets-sheet 5 Jan. 13,1959 l E. c. KOCH Em 2,868,944 l ELECTRIC lFLUID HEATER K Filed June 12,1957 4 '7 Sheets-Sheet 6 INVENTORS Ease/v5 C. KOCH A/EL B//V .l RAYATTORNEY E. c. KOCH ETAL ELECTRIC FLUID HEATER Jan. '13, 1959 Filed June12, 1957- '7 Sheets-Sheet 7 United States Patent ELECTRIC FLUID HEATEREugene C. Koch, Richmond Hill, N. Y., and Kelvin J.

Ray, Ramsey, N. J., assignors to Foster Wheeler Corporation, New York,N. Y., a corporation of New York Application June 12, 1957, Serial No.665,292

13 Claims. (Cl. 219-38) This invention relates to heat exchangers andmore particularly to fluid heaters wherein fluid is heated by means ofelectric heating elements'.

In electrical fluid heaters -of the type disclosed in United StatesReissue Patent No. Re. 23,795, dated March 2, 1954, a plurality oftubular electrical resistance elements are supported in spaced parallelrelationship to each other in the shell or housing of the fluid heaterby a plurality of spaced metal tube sheets through which the electricalresistance elements pass. The electrical resistance elements areconnected at one end to a source of electrical current through a bus andat the other end are grounded to the shell of the heater through anotherbus. The electrical resistance elements pass through bushings or collarsof dielectric material at the tube sheets to electrically insulate theresistance elements from each other and the shell. Fluid to be heatedenters the fluid heater through an inlet means in the shell and flowsthrough the resistance elements, and is thereby heated. The heated fluidpasses from the shell through an outlet means therein to a place lofuse. Control of outlet temperature of the fluid to be heated is effectedby regulating electrical current flow through the resistance elements.It has been found that rapid and accurate control of outlet temperaturecannot be achieved solely by control of electrical input to theresistance elements nor can a substantially constant outlet temperaturebe achieved. Another disadvantage of the aforedescribed fluid heater isthe difficulty in electrically testing the resistance elements, sincethe resistance elements are grounded to the shell. A furtherdisadvantage is the relatively frequent short circuiting of theresistance elements through the tube sheets and shell by reason of thestructural failure of the dielectric bushings which insulate eachresistance element from the tube sheets.

Accordingly, one of the objects of this invention is to provide anelectricfluid heater of substantially the same overall size asconventional electric fluid heaters, such as disclosed in the aforesaidreissue Patent No. Re. 23,795, but having greater heat transfercapacity.

Another object s to provide an electrical fluid heater capable ofoperating at very high temperatures and pressures.

A further object of the present invention is to provide an electricalfluid heater wherein fluid outlet temperature can 4be accuratelymaintained.

Another object of this invention is to provide an electric fluid heaterin which electrical short-circuit of the heating elements is obviated.

A still further object of the present invention is to provide a fluidheater in which the heating elements can be quickly and easilyelectrically tested without the necessity of removing the heatingelements.

The present invention contemplates a novel fluid heater having an outershell or housing and fluid inlet means in the shell for passing fluid tobe heated into the shell. The outer shell also is provided with a fluidoutlet to pass heated fluid from the heater. A plurality of elec-2,868,944 Patented Jan. 13, 1959 ice trical resistance elements aresupported and electrically insulated from each other within the shell bya plurality of tube sheets of dielectric material. Each of theelectrical heating elements comprises two tubular members arranged incoaxial relationship to each other with the inner surface of the outertubular member and the outer surface of the inner tubular member spacedfrom each other to provide an annular passageway. The electrical heatingelements are electrically connected to provide a three phase electricalcircuit, the heating elements of each phase being grounded outside ofthe shell. A baflle means is provided in the shell to provide flow offluid to be heated from the fluid inlet means to the electrical heatingelements. Fluid to be heated flows through the inner tubular members ofthe electrical heating elements and the annular passageway between thetwo tubular members of the heating elements and is thereby heated. Acylindrical member, defining a mixing chamber and having inlet means, isdisposed in the shell in communication at one end with the heatingelements to receive heated fluid from the latter and at the other endwith the fluid outlet in the shell. A second fluid inlet means isprovided in the shell for passing a regulated quantity of relativelycool fluid into the mixing chamber through the inlet means and intoadmixture with heated fluid.

In a second embodiment of the present invention, the dielectric tubesheets supporting the heating elements are each provided with aperturesdisposed between the apertures through which the electrical resistanceelements pass to thereby provide for flow of fluid to be heated alongthe outer surface of the outer tubular members, as

. well as flow through the tubular members.

` The inventionl will be more fully understood from the followingdetailed description thereof when considered in connection with theaccompanying drawings wherein two embodiments of the invention areillustrated by way of example and in which:

Fig. 1 is a longitudinal sectional view of part of the fluid heateraccording to this invention;

Fig. 2 is a longitudinal sectional view of part of the fluid heaterwhich is not shown in Fig. 1;

Fig. 3 is an enlarged fragmentary view of the fluid inlet end of theheating elements showing the means for electrically connecting theheating elements to the electrical input terminals;

Fig. 4 is a view in section taken along line 4-4 of Fig. 1, somewhatenlarged, showing the means for electrically connecting the heatingelements together;

Fig. 5 is a view in section taken along line 5-5 of Fig. 4;

Fig. 6 is a view in section taken substantially along line 6-6 of Fig.2, somewhat enlarged;

Fig. 7 is an enlarged sectional view of the means for electricallyconnecting terminal rods to first heating elements taken along line 7-7of Fig. 8;

Fig. 8 is a sectional view taken along line 8 8 of Fig. 2, somewhatenlarged;

Fig. 9 is a view in section taken along line 9-9 of Fig. 8;

Fig. l0 is a transverse sectional View taken along line 10-10 of Fig. 1ladjacent a tube sheet of a fluid heater according to a second embodimentof the invention;

Fig. 11 is a sectional view taken along line 11-11 of Fig. 10; and,

Fig. 12 is a schematic drawing of the fluid heater according to thisinvention, showing the heating elements, the electric-circuit involved,and the means for introducing fluid into the heater.

Like reference characters in the several views refer to like parts.

Referring now to the drawings, and more particularly Figs. l and 2, 10designates a hollow shell or housing having a central body portion 11and opposite end portions 12 and 13. End portions 12 and 13 are oflarger external cross sectional dimensions than central portion 11 sothat the external surface of end portions 12 and 13 project beyond theexternal surface of body portion 11.

. rhe internal cross sectional dimension of end portion 13 (Fig. 2) isthe same as that of the central portion 11 so that the internal surfaceof end portion 13 is coextensive with the inner surface of centralportion 11. The internal cross sectional dimension of end portion 12(Fig. l) is substantially less than that of central portion 11 to denean opening 14. The inner surface of end portion 12 tapers outwardly fromthe surface defining opening 14 to the inner surface of central portion11. A high pressure cover plate 15 is secured to end portion 13 by aplurality of circumferentially spaced bolts 16 while end portion 12 isprovided with a plurality of circumferentially spaced tapped holes 17 toreceive bolts (not shown) to secure an adapter member (not shown) forconnecting shell 141 to a duct or other apparatus which is to receiveheated fluid.

The inner surface of shell 19 is lined with heat insulating material 18,such as glass wool. The insulating ma terial is held in place againstthe inner surface of shell 10 by a perforated liner 19 having aconfiguration conforming to the inner surface of shell 10. Liner 19 isprovided with perforations so that pressure is equalized on both sidesof the liner, thus enabling the use of a liner of relatively thin gagematerial. Liner 19 is maintained in spaced relationship to the innersurface of shell 10 by a plurality of circumferentially spaced ribs 20(shown in Figs. 3, 6 and 8) which extend radially from the liner 19 toshell 10 and substantially the entire length of body portion 11 and ofend portion 13 of shell 10. As shown, ribs 2h are disposed along thelower circumference of liner 19 but if the fluid heater is intended tobe used in a vertical position, ribs 2t) would be disposed along theentire circumference of liner 19.

A tubular inner 'shell 21 of sheetmetal, or lthe like, having smallercross sectional external dimensions than lin-er 19 is disposed in shell10 in coaxial relationship with the latter. One end of shell 21terminates at a point short of end portion 13 of shell 10 to denebetween the end of shell 21 and end portion 13 a chamber portion A andat the opposite end terminates short of end portion 12 of shell 10. Aplurality of circumferentially spaced ribs or tins 22 are secured toshell 21 and extend the length of shell 21 and radially therefrom toliner 19 in substantial alignment with ribs 2i) of liner 19. As bestshown in Figs. 4, 6 and 8, ribs 22 are spaced along the lowercircumference of shell 21, but if the fluid heater is to be arrangedvertically, ribs 22 would be disposed along the entire circumference ofshell 21. Ribs 22 maintain shell 21 in spaced relationship with theinner surface of liner 19 to thereby provide an annular pas'- sageway Swhich communicates at one end with the space formed between shell 21 anden'd portion 12 and at the other end with chamber A. inner shell 21 isopen at one end (Fig. 2) to communicate with chamber ..A, and at theopposite end (Fig. l) has a fru'st'o-conical end member 23 which tapersinwardly to an open ended cylindrical end portion 24. A hollow mixingcylinder is secured at one end, as hereinafter more fully described,within end portion 24 of inner shell 21. Cylindrical end portion 24 hasa flanged end portion 26 which, when cylinder 25 and end member 23 ofinner shell 21 are locked together, abuts an annular flange member 27.Flange member 27 is welded to cylinder' 25 and is bolted, adjacent itsouter periphery, to an annular ring 28 which is connected to the innersurface of shell 10 and extends therefrom to a point short of cylinder25. Flange 27 and annular ring 2S form a partition 29 which seals offpassageway S from the space B formed between the end of shell 21 and endportion 12 Vof shell 1i).

Mixing cylinder 25' is provided 'at its end, adjacent to inner shell 21,with two spaced bayonet slots 30 (only one of which is shown). Endportion 24 of inner shell 21 is provided with spaced pins 31 (only onebeing shown in the drawings) which pins extend from the inner surface ofend portion 24'. Mixing cylinder 25 is secured Within end portion 24 byinserting cylinder 25 axially within end portion 24 so that pins 31fuliy enter slots 30. Thereafter, cylinder 25 is rotated clockwise, asviewed from end portion 12, to lock cylinder 25 to end portion 24. Theend of cylinder 25, opposite from slots Si), tits within one end of ahollow cylindrical extension member and is secured thereto by two pins33 which are carried by extension member 32 and extend into twolongitudinal slots in the end of cylinder 25 to allow for ditferentialexpansion and contraction between extension member 32 and cylinder 25.The opposite end of extension member 32 extends into opening 14 of endportion 12 of shell 1i) and terminates ilush with the outer end surfaceof end portion 12. Extension member 32 is suitably supported withinopening 14 as by a ring 34 disposed transversely in said opening 14 andsecured, as by welding, to end portion 12 and extension member 32.Mixing cylinder 25 is provided to the left of partition 29, as viewed inFig. l, with a plurality of spaced inlet openings 35 which communicatethe interior of the mixing cylinder 25 with space B. The purpose andfunction of cylinder 25 and inlet openings 35 will be hereinafter fullydescribed.

A fluid inlet nozzle 36 is secured to the right of partition 29, asviewed in Fig. l, by welding or the like, at 36a within an opening 38 inshell 10 and liner 19 so that nozzle 36 communicates with passageway S.Another fluid inlet nozzle 37 is secured to the left of partition 29, asviewed in Fig. 1, by welding, or the like, at 37a within an opening 4t)in shell 1@ and liner 19. Inlet nozzle 36 is connected to a source ofhigh pressure iluid to be heated, as for example air, or any other fluidhaving proper dielectric properties. Inlet nozzle 37 is connected toreceive high pressure fluid, from the same source as nozzle 3'6 or froma different source of fluid.

A plurality of electrical tubular heating elements 41 are supported inspaced parallel relationship to each other within inner shell 21 by aplurality of tube sheets 42 transversely disposed in inner shell 21 andpositioned at spaced points along the length of shell 21. The endmosttube sheet 42, adjacent end portion 13 of shell 10, will be hereinafterdesignated by the reference character 42A. Each tube sheet 42, includingtube sheet 42A, is dimensioned so that it fits snugly but movably withinshell 21. Preferably, each tube sheet 42 and tube sheet 42A is composedof a dielectric material having high resistance and strength at hightemperatures and pressure, as for example, alumina or Vfused silicaquartz. Each tube sheet 42 and tube sheet 42A is provided with aplurality of circumferentially spaced slots 43, as for example, six innumber, as shown in Figs. 8 and l0, which extend inwardly from theperipheral edge of the tube sheet. rl`ie rods 44, corresponding innumber to the number of slots 43 in each tube sheet, are disposed inslots 43, as shown in Figs. 4, 8, 9 and l0. To secure each tube sheet inposition within inner shell 21, an annular ring 45 (Figs. 3, 4, 8 and9)is disposed in close spaced relationship with one side of the tube sheetand is welded to tie rods 44. On the other side of each tube sheet, inclose spaced relationship therewith, a semi-circular ring 46 is secured,as by welding to the lower half of shell 21 and a second semi-circularring 47 is secured, as by welding, to the upper half of shell 21 inclose spaced relationship to the tube sheet. Each tie rod 44, as shownin Figs. l and 2, comprises a center section 48 and end sections 49 and50. which sections are joined together by two sleeves 51 (Fig. l) and 52(Fig. 2). Each tie rod section 4:9 is secured, as by welding, orthelike, in one end of sleeve 51 while end -tie rod section is secured,as by welding, or the like,'in one end lofsleeve 52, the center tie rodsection 43 being free to-'move longitudinally withinvthe-other end ofsleeves 51 and 52. The tie rod sections thus joined together, allow forlongitudinal differential expansion of the tie rods and inner shell 21.

Each tube sheet 42, including tube sheet 42A, is provided with aplurality of spaced openings 53 to receive therethrough tubular heatingelements 41 and a centrally positioned opening 55 to receive a tubularground member 56. Tubular ground member 56 is of electrical resistormaterial7 as for example, nickel-chromium alloy or other suitablematerial. Tube sheet 42A and the next adjacent tube sheet 42, inaddition to openings 53 and opening 55, are each provided with threespaced openings disposed near the peripheral edge of the tube sheets toreceive three terminal rods 57 (see Figs. 3, 6, 8 and l2). Terminal rods57 are only long enough to extend through tube sheet 42A and the nextadjacent tube sheet 42, the terminal rods 57 being supported by theaforesaid ytube sheets.

Each tubular heating element 41 comprises an outer tube 60 and an innertube 61, each of which are of electrical resistor material, for example,nickel-chromium alloy or other equivalent electrical resistor material.Inner tube 61 is of smaller external diameter than the internal diameterof tube 60, and is arranged within outer tube 6i) in coaxialrelationship with outer tube 60 to define between the inner surface ofthe outer tube 60 and the outer surface of inner tube 61 a fluidpassageway 62. To maintain inner tube 61 in coaxial and spacedrelationship to outer tube 69, a plurality of radial spacer members orfins 63 are positioned at various points along the length of tube 61 andextend radially from the outer surface of tube 61 to abut against theinner surface of outer tube 60 (Fig. 3). Outer tubes 60 are of equallength and have their opposite ends extending to a point beyond tubesheet 42A and the opposite endmost tube sheet 42, while inner tubes 61are of equal length and have their opposite ends extending to a pointbeyond the opposite ends of tubes 60. Tubular ground member 56 is ofsuch a length that one end thereof extends from tube sheet 42A beyondthe ends of tubes 61 and the opposite end terminates beyond the oppositeendmost tube sheet 42 in the same plane as the ends of outer tubes 60.

As best shown in Fig. l2, heating elements 41 are arranged to form athree-phase electrical circuit. Each phase, hereinafter designated P1,P2 and P3, comprises a plurality of heating elements 41, a terminal rod57 and the tubular ground tube 56, which members in each phase areconnected together in parallel or serially connected together asillustrated in the drawings and as hereinafter described. A firstelectrical heating element 41 of each phase is connected by anelectrical connector means 64 to a terminal rod 57 in each phase.

Each electrical connector assembly 64, as best shown in Figs. 3 and 7,comprises two rectangular blocks 65 and 66 of electrical conductingmaterial which are secured in spaced relationship to each other by aspacer member 67 which extends between blocks 65 and 66. Spacer member67 is secured, as by welding, at one end to the center of block 65 andat the other end is provided with an axial hole 68 which is threaded toreceive a bolt 69. Block 66 is provided with a hole to receivetherethrough bolt 69 which is threaded into tapped hole 68 to therebysecure blocks 65 and 66 together. Block 65 is provided with twotransverse holes 70 and 71 which are respectively adapted to receivetherethrough the end of outer tube 6) of a rst electrical heatingelement 41 and the end of terminal rod 57. Block 65 is secured, as bywelding, around holes 7@ and 71 to outer tube 60 of the first electricalheating element 41 and to the terminal rod 57, respectively. Block 66 isprovided with a hole 72, adjacent one end thereof, which hole is adaptedto receive therethrough the end of inner tube 61 of the first electricalheating element Lift. Block 66 is secured, as by welding, around theperiphery of hole 72 to the inner tube 61, while the oppositev end ofblock 66 is provided with a 6 concavity adapted to engage part oftheperipheral surface 0f terminal rod 57, block 66 being secured along theconcavity, as by welding, to the terminal rod.

The opposite end of each first electrical heating element 41 iselectrically connected to the next adjacent electrical heating element41 in each of the phases P1, P2 and P3, by electrical connector members73 and 74, as best shown in Figs. 4 and 5. Flexible connector members 73comprise a flat strap of electrical conducting material, as for example,wire braided strap or nickel, which is looped and is suitably secured,as by welding, at one end to the outer tube 60 of the first electricalheating element and at the other end to outer tube 60 of the nextadjacent electrical heating element 41. Connector member 74 is a flatstrip of electrical conducting material, as for example, a low carbonnickel, which is looped and suitably secured at one end to the innertube 61 of the first electrical heating the ends of outer tubes 60 ofadjacent heating elements,

41 which are to be connected together. Block 76 has a spacer member 77,similar to spacer member 67, secured thereto, as by welding, whichspacer member is provided with an axially extending tapped hole. Anotherblock 78, slightly smaller in dimensions than block 76, is secured tospacer member 77 by a bolt threaded into the tapped hole in spacermember 77. Block 78 is provided with two spaced holes which are adaptedto receive therethrough the ends of the inner tubes 61 of adjacentheating elements 41 which are to be connected together. Block 76 issecured, as by welding, to outer tubes 60 of the adjacent heatingelements around the periphery of the holes in block 76, while block 78is secured, as by welding, to the inner tubes 61 of the adjacent heatingelements around the periphery of the holes in block 78. The remainingheating elements 41 in each phase P1, P2 and P3 are serially connectedtogether as hereinbefore described by connector members 73 and 74 andconnector assemblies 75.

As best shown in Figs. 4 and 5, a fiat metal strip 80 of high electricalconductivity, as for example, nickel, is electrically connected, as bywelding, to the end portion of each of outer tubes 60 of the lastserially connected heating element 41 in each of the three phases. Eachstrip 80 is coextensive with the heating element to which it is securedand extends to a point beyond the ends of inner tubes 61. Strips 80 haveend portions Si bent to extend in a direction toward each other. StripsSi) are interconnected by a triangular-shaped plate 32 of electricalconducting material, as for example, nickel, having a triangular-shapedcentral opening 83. Plate 82 is provided wi-th three projecting tabs 84which extend normal to the plate. Plate S2 is dimensioned so that tabs84 lie in surface Contact with the outer surface of strips Si), tabs 84being secured to strips 80, as by welding, to thereby electricallyconnect together outer tubes 6i) of each of the last heating elements 41in each phase. A flexible connector 86, such as a wire braided strap, isprovided for each inner tube 61 of the last heating elements in eachphase. Each connector S6 is electrically connected at one end, as bywelding, to an inner tube 61 and at the other end at 85 to an endportion 8l of a strip Sti. In this manner, each of the inner tubes 6l iselectrically connected at S5, through end portions 8l of strips 80, toplate 82. To connect outer tubes 6l) and inner tubes 6l of the lastheating elements 4l in each phase to ground tube 56, a channel member87, U-shaped in cross section, is secured at one end to the end of'ground tube 56 so as to extend coextensively with the latter, throughopening 83 in plate 82. Channel 87 is of metal having high electricalconductivity, as for example, nickel. Channel 87 is electricallyconnected to plate S2 by means of a looped ilexible connector 3S, as forexample, wire braided strap, which is secured at one end, as by welding,to one of the tabs S4 of plate 82 and at the other end to channel 87.The aforedescribed means for electrically connecting the last heatingelements 4l in each phase to ground tube 56 while effectively connectingthe inner and outer tubes of each oi the last heating elements 41 toground tube 56, provides at the same time, means for allowingdifferential expansion'between the outer tubes 6u and inner tubes 6l andbetween outer tubes 6u and ground tube 56. The differential expansionand contraction between-the outer tubes ntl and inner tubes 6l arecompensated for by flexible connectors 86 while relative contractionvand expansion of ground tube 56 and outer tubes d() is compensated forby tlexible connector 8d.

Electrical heating elements 4l are each secured within tube sheet @2Aagainst longitudinal movement as best shown in Figs. 2 and 9, by acollar 89 which is passed over the end of outer tube dll and is secured,as by welding, to the outer tube adjacent the outer surface of tubesheet 42A. A second collar 9b is positioned on tube d@ adjacent theinner surface of tube sheet 42A, and is securedte outer tube 60 by meansof a set screw 91. Collars 39 and 9u secured to tubes 60 on either sideof tube s eet 42A prevents endwise misalignment of tubes 6% relative totube sheets "l2 and tube sheet 42A. Since the inner tubes 6l are securedto outer tubes 6? by connector assemblies d4 and 7S, inner tubes 6l arealso held against endwise misalignment relative to tube sheets 42 andtube sheet 42A. Because outer tubes 6d and inner tubes 6l are xedagainst linear movement with respect to tube sheet 42A, linear expansionand contraction of outer tubes 6i) and'inner tubes 6l will be in adirection toward the lett as viewed in Figs. l and 5, and for thisreason, differential expansion between outer tubes 6l) and inner tubes6l will be manifested at the tube end portions adjacent end portion l2of shell lil. To allow for this dilterential expansion, outer tubes 6band inner tubes 61 are separately connected together, connector members'73 connecting outer tubes 60, while inner tubes 6l are connectedtogether by connector members 74. ln addition, flexibility of connectormembers '73 allows for relative expansion and contraction between outertubes 60 which are electrically connected together while the flexibilityot' connector members 72% allows vfor differential expansion andcontraction of inner tubes 6l which are electrically connected togetherby connector members 7d.

ln shell lil, adjacent end portion 1l3, three electrical input terminals92 and a ground terminal 93 are disposed in circumferential spacedrelationship to each other and secured in openings 94 in shell llt).(see Figures 3 and 6). input terminals 92 and ground terminal 93 areidentical in construction, cach comprising a base member 95 having acentral opening 9e and a recessed outer surface to provide a shoulder97. A disc 9S of insulating material, as for example, alumina, having acentral opening 99 is inserted in the recess against a gasket 93A whichlies against shoulder 97 of base member 95. A terminal post lil@ isprovided with a plate lill which is secured to the post between itsopposite ends. Terminal post lili) is inserted axially through openings99 in disc 93 and opening 96 in base member until plate 'lill inipingesanother gasket which is disposed against the outer surface ot dise 9".Another insulating disc lilZ, similar to disc and having a centrallydisposed opening. passed over the outer end of terminal post itl and isheld against plate lill by a hold-down plate lr03. Plate 163 is providedwith a central opening adapted to receive therethrough terminal postltltl. A plurality of bolts ltll extend through circumterentially spacedholes in Cir hold-down plate 103 and are threaded into tapped holes inbase members 95. When bolts lull are turned into tapped holes in basemember 95, hold-down plate lr03 and base member 9S are drawn togetherthereby causing insulating discs 98 and 102 to be respectively clampedbetween plate ll and base member and between plate lill and hold-downplate 193. Tightening bolts 101i also squeezes gaskets 98A and 98Bbetween base member 95, disc 98 and plate 101' to thus provide apressure-tight assembly. An insulating sleeve m5 is passed over theouter end c--f terminal post and into the openings in hold-down plate103 and disc ltlZ to electrically insulate terminal post ltlil fromhold-down plate 103 and thereby prevent electrical arcing between thepost and hold-down plate 103. The opposite end portions of terminalposts lltlll'are threaded to receive electrical connectors.

As best shown in Figs. 3 and 6, input terminals are each electricallyconnected to a terminal rod 57 by means of a flexible connector 166, asfor example, a multilayer braided strap',.having secured at one end asplit clamp 107 and atithe other end a split clamp ltll. Connector 106is connected to terminal post ltltl by tightening split electrical clampll7 to the inner threaded end portion of the terminal post. At the otherend, connector M6 is secured to terminal rod S7 by fastening split clamp108 to the end portion of the terminal rod. Similarly, terminal postlill) of ground terminal 93 is connected to ground tube 55. A flexibleconnector M9, as for example, a multilayer braided strap, having securedat one end a split clamp lll@ and at the other end a split clamp ill,electrically connects terminal post lull of ground terminal 93 andground tube 5d by tightening split clamp il@ to the threaded end portionof terminal rod ldd and securing splitclamp lll. to the end portion ofground tube 56. The outer end portions of terminal posts le@ ot' inputterminals 92 are connected to receive electrical power while terminalpost lull of ground terminal 93 is connected to the ground. Terminalposts Mld are connected to terminal rods 57 rather than directly toheating elements il so that a permanent electrical power connection tothe heating elements is eiected and free expansion and contraction ofthe tube bundle is allowed.

As shown in Fig. ll, electrical power is Supplied from a source ofelectricity 112, such as an electric generator H3, to the primary coillill of three transformers lle, li? and llt; by way of line i115. rl`hesecondary coils H9 of transformers lla, M7 and Tilt? are respectivelyconnected by way of lines 129, 122, l2?. to a saturable reactor 123which controls voltage and current flow to each of the input terminalslili). Electrical current )flows from saturable reactor 23 via lineslZd, 125 and i126, throught a 3-pole single throw switch 12'? whenclosed, to input terminals 92. Ground terminal 93 connected by way ofline 123 to a ground disconnect switch i129, the switch 129 beinggrounded at It?,

All electrical heating elements are thus connected in a three-Jhaseelectrical circuit having a commen ground and may be supplied from acommon source of power EEZ, as described. Electrical current in each ofthe L.. ses P1, P2 andV P3 i'lows from terminal posts illu of inputterminals 92 through flexible connector' to the terminal rods 57 in eachphase 3). 'lhereaiteu current flows from the terminal rods to outertubes del and inner tubes 6l of the lirst electrical heating elements 4iof each phase by way of connector assembly o (Fig. 7) to thereby heatthe tubes eti and di.. The current liows from outer tubes o@ and inr rtubes or^ the first electrical heating elements to the outer tubes d@and inner tubes 6i of the next adjacent heating elements of phases P1,if'g and P3 by way of connector members 73 and 74 (Figs. 4 and 5). Afterflowing througl the adjacent heating elements 4l, the current flows toouter tubes 6l) and inner tubes 6l of the next successive heatingelements il through connector assemblies 75 (Figs.

3, 8 and 9). Thereafter, electric current continues to flow in seriesthrough the remaining heating elements in each phase to and through thelast heating elements 41 in each phase. Current then ows from outertubes 60 and inner tubes 61 of each of the last heating elements 41 ineach phase, through strips 80, connectors 86, plate 82, connector 88 andchannel 87 to ground tube 56 (Figs. 4 and 5). At the other end of groundtube 56, current ows therefrom by way of connector 109, terminal post100 of ground terminal 93 and line 128 to ground 130.

Operation Electrical heating elements 41 in each of the phases areheated by flow of `electrical current therethrough as aforedescribed.Fluid to be heated, as for example, air at 80 F., is introduced underhigh pressure, as for example 4,000 p. s. i. g., into shell 10 throughvalve line 131 (Fig. 12), line 132, valve 133 and inlet nozzle 36 (Figs.1 and 12). From inlet nozzle 36, the fluid iiows through annularpassageway S between the inner shell 21 and liner 19 and istherebypreheated by heat radiating from inner shell 21. Outer shell 10is insulated from the high temperatures bythe cool fluid owing throughpassageway S and heat insulating layer 18. From passageway S, the uidflows into chamber A and into and through inner tubes 61, annularpassageways 62, formed between outer tubes 60 and inner tubes 61 ofheating elements 41, and ground tube 56. Fluid in passing throughelectrically heated inner tubes 61 absorbs heat therefrom by conductionand radiation from the inner surface of tubes 61 while fluid flowingthrough passageways 62 absorbs heat by conduction and radiation from theouter surface of tubes 61 and from the inner surface of tubes 60. Fluidin passing through ground tube 56 is heated by conduction and radiationof heat from the inner surface of the ground tube. Heated fluid passesfrom heating elements 41 and ground tube 56 into the frusto-conical endmember 23 of inner shell 21, thence `through cylindrical portion 24 intomixing cylinder 25.

A controlled amount of relatively cool fluid, such as air, underpressure and at a relatively low temperature, as for example, 80 F., isadmitted through a valve 134 in line 131, a line135 connected to line131, and inlet nozzle 37 (Fig. l2) and thence into space B which isformed between partition 29 and end portion 12 of shell 10. Since spaceB communicates, through openings 35 in mixing cylinder 25, with theinterior of cylinder 25, cool iluid ilows from space B through openings35 into cylinder 25 and into admixture with heated iluid owing fromheating elements 41. The use of a mixing cylinder 25 and the position ofopenings .35 with respect to heated uid ilow and nozzle 37 is for thepurpose of providing sufficient turbulence within cylinder 25 to insureintimate mixing of the cool iluid and heated fluid. Intimate mixing ofthe two uids provides a fluid mixture at the heater outlet which is ofsubstantially uniform temperature throughout its ow area. The mixture ofiiuid passes from cylinder 25 into extension member 32 and passes out atthe opposite end thereof at a relatively high temperature, as forexample, 1600 F. into an adapter member (not shown) which in turn isconnected to conduit means for passing the heated uid to aplace of use.

The iiuid heater of this invention is operated to deliver apredetermined quantity of heated uid, which quantity is less than thetotal desired quantity, to mixing cylinder 25 at a temperature above adesired outlet temperature. An amount of relatively cool uid, equal tothe difference between the amount of heated fluid delivered to mixingcylinder 25 and the total desired quantity, is introduced through nozzle37 into admixture with the heated fluid within cylinder 25 to therebyprovide the total desired quantity of heated uid at the desired outlettemperature. Furthermore, should it be desired to quickly provide fluidat a lower outlet temperature, a greater amount of cool fluid may beadmitted into mixing cylinder 25 through l0 line 131, valve 134 andnozzle 37 with a commensurate reduction in the quantity of fluid flowingthrough lines 131 and 132, valve 133, nozzle 36 and heating elements 41by reducing flow of iluid through valve 133. Similarly, if it is desiredto rapidly provide fluid at a higher outlet temperature, a greaterquantity of fluid may be circulated through heating elem-ents 41 byincreasing flow of fluid through valve 133 with a lesser quantity ofcool fluid being admitted through nozzle 37 by reducing the opening invalve 134. Under normal operating conditions, as aforedescribed, valve136 is closed. In addition, secondary control of outlet temperature maybe effected by control of current flow through heating elements 41 byadjustment of saturable reactor 123.

Modification Another embodiment of the present invention is shown inFigs. 9 and l0, which embodiment is similar to the fluid heaterdescribed and shown in Figs. 1 to 9, inclusive, and l2, except that tubesheets 42, including tube sheet 42A, are each provided with a pluralityof diamondshaped openings 138 to form a lattice-like structure. Heatingelements 41 are supported in various openings 138, as shown, so thatthey extend in lateral spread relationship. Fluid to be heated, as forexample air, ilows through inner tubes 61 and passageways 62 which areformed between inner tubes 61 and outer tubes 60 of each of the heatingelements 41, as well las through open ings 138 in tube sheets 42 andtube sheet 42A. Fluid to be heated which is flowing through openings138, ows between tubes 60 and absorbs heat by radiation and conductionfrom the outer surface of tubes 6i). Since tube sheets 42 and tube sheet42A according to this embodiment, permit passage o-f iluid to be heatedbetween the heating elements 41 as well `as through them, the pressuredrop through the inner shell is greatly reduced and the heat transfer isincreased by utilizing the outer surface of tubes 60 for heating fluid.Thus, a greater quantity of fluid may be heated than in the otherembodiment of this invention.

It can readily be seen, from the foregoing description, that a fluidheater has been provided for heating a greater quantity of uid withoutan appreciable increase in its overall size. This increased capacity isaccomplished by novel electrical heating elements which have one tubewithin another and by arranging the electrical heat ing elements in athree phase electrical circuit. In addition, all of the electricalheating elements of the fluid heater may be electrically tested bymerely inserting a megohmmeter in ground line 128 to test the insulationvalue and for change in resistance of the heating elcments. This testmay be made after each run or periodically, and in this manner, imminentbreakdown can be anticipated and corrective measures undertaken beforeactual failure. Furthermore, the electrical heating elements of eachphase may Ibe separately tested for change in insulation value andchange in resistance which would indicate imminent breakdown of one ormore of the heating elements in the phase being tested.

The iluid heater of this invention has relatively long operative life,since short circuiting of the heating elements through the tube sheetsis obviated by providing tube sheets of dielectric material.

Although two embodiments of the invention have been illustrated anddescribed in detail, it is to be expressly understood that the inventionis not limited thereto. Various changes can be made in the arrangementof parts without departing from the spirit and scope of scope of theinvention, as the same will now be understood by those skilled in theart. As for example, inner shell 21 may be dimensioned so that it liesagainst liner 19, thus eliminating passageway S, and fluid inlet 36 maybe disposed in the shell in direct communication with chamber A todeliver uid to be heated directly to heating elements 41 withoutdeparting from the spirit and scope of the present invention.

What is claimed is:

1. A fluid heater of the class described, comprising a shell, aplurality of electrical heating elements disposed in said shell, meansfor supporting said elements in spaced parallel relationship to eachother and electrically insulating said elements from each other and fromthe shell, each of said elements comprising a first tube and a secondtube of smaller diameter than said first tube, said second tube arrangedin coaxial relationship with said first tube and spaced from the latterto provide an annular passage between the inner surface of said firsttube and the outer surface of Said second tube, an electrical inputmeans connected to a source of electrical current and to a first of saidheating elements for delivering electrical current to the latter, saidheating elements being connected together to provide series liow ofelectric current, an electrical ground means in said shell connected toa last of said heating elements to complete the electric circuit throughthe resistance elements, said electrical input means and said groundmeans being electrically insulated from said shell, a liuid inlet meansfor passing liuid to be heated into said shell, baie means for directingflow of fluid to be heated into one end of said second tube and into theannular passage formed lbetween the first and second tubes of each ofsaid heating elements, and fluid outlet means communicating with theother end of said second tube and said passage be tween the first andsecond tube of each of the heating elements to receive heated fluid fromthe latter.

2. A heat exchange apparatus of the class described, comprising ahousing, a plurality of electrical heating elements, means forsupporting said elements in spaced parallel relationship to each otherin said housing, means for electrically insulating said heating elementsfrom each other and the housing, said heating elements being arranged ina plurality of groups, an electrical terminal member disposed in saidhousing and insulated therefrom for each group of heating elements, anelectrical ground terminal disposed in and insulated from said housing,each of said heating elements include a first tubular member and asecond tubular member of smaller diameter than said first tubular memberarranged within the other in coaxial relationship, means forelectrically connecting said first and second tubular members of a firstheating element of each group to the input electrical terminalassociated with the group, means for connecting said first and secondtubular members of each of the heating elements of each group for seriesflow of electrical current therethrough, another means for electricallyconnecting said first and second tubular members of a last heatingelement of each group to said electrical ground terminal, fluid inletmeans in said housing in communication with said heating elements todeliver liuid to be heated to the latter, `and fluid outlet means insaid housing communicating with the heating elements to receive heatedfluid from the latter.

3. A fluid heater of the class described, comprising a shell, aplurality of electrical heating elements disposed in said shell, each ofsaid heating elements comprising two tubes arranged coaxially one withinthe other and with the outer surface of the inner tube spaced from theinner surface of the outer tube, means for supporting said heatingelements in spaced relationship to each other and for electricallyinsulating said elements from each other and said shell, said heatingelements being grouped in a plurality of electrical circuits, eachelectrical circuit gro-up having a common ground, means for connecting afirst heating element of each circuit to a source of electrical current,second means for electrically connecting each heating element of eachcircuit in series, third means for connecting a last heating element ofeach circuit to said common ground, a fluid inlet in said shell incommunication with said heating elements for delivering fluid to l2 beheated to the latter, and a fluid outlet in said shell in communicationwith said heating elements for receiving heated liuid from the latter.

4. The apparatus of claim 3 wherein the second means for electricallyconnecting each heating element of each circuit in series comprises afirst electrical conductor con nected at one end to the outer tube of aheating element and at the other end to the outer tube of next adjacentheating element, and a second electrical conductor connected at one endto the inner tube of a heating element and at the other end to the innertube of a next adjacent heating element.

5. A fluid heater of the class described, comprising a shell, a tubebundle disposed within said shell, said tube bundle comprising aplurality of first electrical heating elements, a plurality of secondelectrical heating elements, a plurality of third electrical heatingelements, a ground tube, disposed adjacent said heating elements, eachof said first, second and third electrical heating elements comprisingtwo tubes disposed coaxially one within the other and with the outersurface of the inner tube spaced from the inner surface of the outertube, a first electrical input terminal in said shell and insulatedtherefrom, said first input terminal being connected to a source ofelectrical current and to a first heating element of said plurality offirst heating elements to respectively receive and deliver electricalcurrent to the latter, a second electrical input terminal disposed insaid shell and insulated therefrom, said second input terminal beingconnected to a source of electrical current and to a first heatingelement of said plurality of second heating elements to respectivelyreceive and deliver electrical current to the latter, a third electricalinput terminal disposed in said shell and insulated therefrom, saidthird input terminal being connected to a source of electrical currentand to a first heating element of said plurality of third heatingelements to respectively receive and deliver electrical current to thelatter, said plurality of rst heating elements being connected togetherin series, said plurality of second heating elements being connectedtogether in series, said plurality of third heating elements beingconnected together in series, means for electrically connecting a lastheating element of each of said plurality of first, second and thirdheating elements to said ground tube, a ground terminal disposed in saidshell and insulated therefrom, said ground terminal being connected toreceive electric current from said ground tube, liuid inlet means insaid shell arranged to direct fluid to be heated to said rst, second andthird heating elements, and a fluid outlet means in said shell arrangedto receive heated fluid from said rst, second and third heatingelements.

6. The apparatus of claim 5, wherein means for providing a fluid mixingchamber adjacent said outlet means and in communication with the latterand the first, second and third heating elements to receive heated fluidtherefrom, and fluid inlet means in said shell in communication withsaid fluid mixing chamber to deliver relatively cool liuid to the latterinto admixture with the heated fluid to provide heated fluid at apredetermined temperature.

7. A fluid heater of the class described, comprising a shell havinginlet means for receiving fluid to be heated and outlet means fordischarging heated fluid, a plurality of tubular electrical resistanceelements disposed in said shell, a plurality of spaced tube sheetsarranged in said shell to support said heating elements in spacedrelationship to each other and said shell, said tube sheets beingcomposed of dielectric material to electrically insulate said heatingelements from each other and said shell, the heating elements beingconnected together and to a source of electrical current to conductelectrical current, said heating elements being arranged to receivefluid to be heated from said inlet means and to discharge heated liuidto said outlet means.

8. The apparatus of claim 7 wherein the tube sheets are composed ofalumina.

9. The apparatus of claim 7 wherein the tube sheets are composed offused silica.

10. The apparatus of claim 7 wherein the tube `sheets are provided witha plurality of apertures therein to allow flow of uid to be heatedbetween the heating elements.

11. A heat exchange apparatus of the class described, comprising a shellhaving inlet means for receiving iiuid to be heated and outlet means fordischarging heated fluid, a plurality of spaced electrical heatingelements disposed in said shell, each of said heating elementscomprising two tubular electrical resistance members arranged coaxiallyone within the other and with the outer surface of the inner tube spacedfrom the inner surface of the outer tube to provide an annular passagebetween the tubular members, said tubular members of each heatingelement being connected to receive and conduct electrical current to bethereby heated, a plurality of spaced tube sheets disposed in said shelladapted to receive and support said plurality of electrical heatingelements, each of said tube sheets being composed of dielectric materialto electrically insulate said tubes from each other and the shell, eachof said tube sheets being provided with apertures disposed thereinbetween said heating elements to provide for passage of fluid to beheated in heat exchange relationship with the outer surface of the outertubular member of each heating element, bafe means in said shell fordirecting uid to be heated from said inlet means to one end of saidheating elements and to the outlet means.

12. A iiuid heater of the class described, comprising A.

a shell, a plurality of electrical heating elements disposed in saidshell, means for supporting said heating elements within said shell andincluding means for electrically insulating said heating elements fromeach other and said shell, each of said heating elements comprising twotubular electrical resistance members arranged coaxially one within theother and with the outer surface of the inner tubular member spaced fromthe inner surface of the outer tubular member, said tubular members ofeach heating element being connected to receive and conduct electricalcurrent to be heated thereby, uid inlet means in said shell incommunication with one end of said heating elements to deliver fluid tobe heated to the latter, and fluid outlet means in said shellcommunicating with the other end of said heating elements to receiveheated fluid from the latter and to pass heated uid from the uid heater,second uid inlet means in said shell communicating with a source ofrelatively cool uid, a member disposed in said shell and forming amixing chamber, said member having an inlet end portion and an outletend portion, said inlet end portion being connected to receive heatedinid from said heating elements and at the outlet end portion connectedto the outlet means in said shell, and means communicating with saidsecond inlet means and said member to pass relatively cool iiuid fromsaid second inlet means into the mixing chamber and into admixture withthe heated fluid to provide heated luid at a predetermined temperature.

i3. A liuid heater of the class described, comprising an outer shell, aninner shell disposed within the outer shell and spaced therefrom toprovide a passage for uid to be heated, a uid inlet means in said outershell in communication with said passage, a second fiuid inlet means insaid outer shell connected to a source of relatively cool uid, toreceive cool uid from the latter, a plurality of electrical heatingelements disposed within said inner shell and in communication with saidpassage to receive fluid to be heated from the latter, means forsupporting said heating elements in spaced relationship to each otherand for electrically insulating said elements from each other and saidinner shell, each of said heating elements comprising two electricalresistance tubes disposed coaxially one within the other and with theouter surface of the inner tube spaced from the inner surface of theouter tube, the two tubes of each heating element being connected toreceive and conduct electrical current to be thereby heated, a iiuidoutlet means in said shell, a cylindrical member open at both ends andconnected at one end to the inner shell to receive heated uid and at theopposite end to said outlet means, said cylindrical member having aplurality of spaced openings which communicate with said second inletmeans for passing relatively cool iiuid into admixture with heated fluidin said cylindrical member to provide heated fluid at a predeterminedtemperature.

References Cited in the le of this patent UNITED STATES PATENTS Re.23,795 Cartinhour Mar. 2, 1954 1,034,952 Ball Aug. 6, 1912 1,727,585Carleton Sept. 10, 1929

